Sensing a liquid level contained in a tank may be performed utilizing sonic measurement techniques. Typically, sonic or ultrasonic measurements are performed with the use of a piezoelectric crystal. If a liquid level is known and the geometry of a tank is known, then the liquid volume in the tank can be calculated based upon the measured level. However, when the liquid in question is propane and the tank in question is a propane tank, problems arise.
One problem is the adequacy of acoustic coupling between the ultrasonic transducer and the fuel tank. If the coupling is poor, then it may not be possible to obtain a measurement, or any measurement made may be unreliable. Another problem is that dispersion of the transmitted ultrasonic beam may reduce the available reflected energy so much that it is difficult or impossible to obtain a valid reading. Dominating any solution to such problems is the question of cost. A solution which enables direct measurement, but which requires a costly installation on each fuel tank of each customer, is an impractical solution.